Digital data streaming using server driven adaptive bitrate

ABSTRACT

A method and system for server driven adaptive transcoding is provided. A transcoding server computer may initially receive a first portion of a particular media file from a media file repository. The transcoding server computer may transcode the first portion of the particular media file into a first transcoded media segment of a first quality and send the first transcoded segment to a client computing device. The transcoding server computer may receive a second portion of the particular media file from the media file repository, transcode the second portion of the particular media file into a second transcoded media segment of a second quality different than the first quality, and send the second transcoded media segment to the client computing device.

FIELD OF THE DISCLOSURE

The technical field of the present disclosure generally relates tocomputer hardware, software, and systems that implement communicationsbetween client computing devices and server computers. The technicalfield of the disclosure also is computer hardware, software and systemsthat are programmed for transcoding of digital media files.

BACKGROUND

The approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

Digital video streaming over packet-based networks is a common methodfor user computers to view videos that are stored on different devices.Video streaming allows user computers to access and watch a largernumber of videos than could be stored on the user computer. Generally, avideo is stored on a separate server computer and is sent to clientcomputing devices for viewing.

Often, a client computing device is unable to efficiently stream a videostored in its source formatting. For example, a client computing devicemay be unable to download a file as fast as the file is played, therebyforcing the streamed video to pause every time the playback of the filecatches up to the end of the downloaded portion of the file. The abilityof the client computing device to stream videos may be based on aninternet connection, the type of device, the hardware of the device,and/or any other activities being performed by the device. A computerthat is currently downloading a 16 GB file will generally have lowerstreaming capabilities than a similarly situated computer that is notdownloading a 16 GB file.

Due to the inability of many computing devices to stream video files intheir source formatting, video files are often transcoded into differentformats for streaming by different client computing devices. Transcodinggenerally refers to the conversion of a digital file from one encodingto another encoding. Transcoding video files may refer to changing theformat of a video file in order to ensure compatibility with a clientcomputing device, changing the codec of a video file, changing a bitrateof a file, such as by compressing the file, and/or changing a resolutionof a file.

Many streaming services will store multiple versions of digital mediafiles that have been transcoded into different formats, bitrates, and/orresolutions. For example, a video may be transcoded into transcodedversions of the video at 1080p, 720p, and 480p bitrates and stored on aserver computer. If a client computing device requests a stream at 720p,the server computer sends the 720p version of the video to the clientcomputing device.

Storing multiple copies of each video tends to be efficient fordelivering videos that are frequently viewed. For example, a videostreaming service that receives hundreds of requests for a single videoduring a day likely has increased capabilities to store multipleversions of each video on a server computer. The same may not be truefor a personal server computer which is accessed by a few people in ahousehold and receives requests for access to particular video filesrarely. In such cases, storing multiple copies of every single videofile becomes a large drain on the storage of the personal servercomputer. Additionally, much of that storage may be unnecessary as somefiles may never be accessed or may be accessed less than a handful oftimes.

While the server computer could store one transcoded version of eachfile based on the requesting devices, doing so does not take intoaccount changing needs over time. Due to changes in connectivity, aclient computing device may lose the capability to download or streamfiles of a certain size without causing delay in the playback of thefiles. Servers that store multiple versions of the same file are capableof adapting by a streaming a lower quality version of the file when theclient's connection is negatively impacted. A server that does not storemultiple transcoded versions of a file does not retain the capability toadapt to changes in connectivity of the client device.

Additionally, the server computer may be unable to provide the highestquality video file that a client computing device is capable ofeffectively viewing. Thus, a user may be stuck viewing a low qualityversion of a video file because higher quality transcoded versions ofthe video file are unavailable.

Thus, there is a need for a method for providing transcoded versions ofa digital media file that can adapt to capabilities of a clientcomputing device without requiring the storage of multiple transcodedversions of each digital media file on a server computer. Such atechnique would be useful for on-the-fly transcoding of video filesand/or portions of video files.

SUMMARY OF INVENTION

The appended claims may serve to summarize the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 depicts an example networked computer system in which thetechniques described may be practiced, according to one embodiment.

FIG. 2 depicts an example method of adaptive transcoding of a digitalmedia file.

FIG. 3 depicts an example system executing the methods described herein.

FIG. 4 is a block diagram that illustrates a computer system upon whichan embodiment may be implemented.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present disclosure. It will be apparent, however,that embodiments may be practiced without these specific details. Inother instances, well-known structures and devices are shown in blockdiagram form in order to avoid unnecessarily obscuring the presentdisclosure.

General Overview

Systems and methods are provided for transcoding of digital media filesas the files are transmitted via streaming over a digital data network.A digital media file may be stored in a media file repository that isseparate from a client computing device. When the client computingdevice requests the digital media file, a transcoding server computertranscodes a first portion of the digital media file into a transcodeddigital media segment of a first quality and sends the transcodeddigital media segment to the client computing device. If the transcodingserver computer determines that the quality of the digital media fileshould change due to one or more factors, such as the capabilities ofthe client computing device, capabilities of the transcoding servercomputer, load balancing of multiple clients accessing digital mediafiles, or the performance of the network between the client computingdevice and the server computer, then the transcoding server computer maybegin transcoding the next portions of the digital media file intotranscoded segments of different qualities.

In an embodiment, a method comprises receiving, at a transcoding servercomputer, a first portion of a particular media file from a media filerepository; transcoding the first portion of the particular media fileinto a first transcoded media segment of a first quality; transmittingthe first transcoded media segment to a client computing device;receiving, at the transcoding server computer, a second portion of theparticular media file from the media file repository; transcoding thesecond portion of the particular media file to a second transcoded mediasegment of a second quality that is different than the first quality;sending the second transcoded media segment to the client computingdevice.

Structural Overview

FIG. 1 depicts an example networked computer system in which thetechniques described may be practiced, according to one embodiment.

In the example of FIG. 1, a client computing device 120 and atranscoding server computer 130 are communicatively coupled to a datacommunications network 100. The network 100 broadly represents anycombination of one or more data communication networks including localarea networks, wide area networks, internetworks or internets, using anyof wireline or wireless links, including terrestrial or satellite links.The network(s) may be implemented by any medium or mechanism thatprovides for the exchange of data between the various elements ofFIG. 1. The various elements of FIG. 1 may also have direct (wired orwireless) communications links. The client computing device 120,transcoding server computer 130, and other elements of the system eachcomprise an interface compatible with the network 100 and are programmedor configured to use standardized protocols for communication across thenetworks such as TCP/IP, Bluetooth, and higher-layer protocols such asHTTP, TLS, and the like. As described further herein, a media filerepository 140 may be hosted on the transcoding server computer 130and/or on a separate server computer.

Client computing device 120 is a computer that includes hardware capableof communicatively coupling client computing device 120 to one or moreserver computers, such as transcoding server computer 130 over one ormore service providers. For example, client computing device 120 mayinclude a network card that communicates with transcoding servercomputer 130 through a home or office wireless router (not illustratedin FIG. 1) coupled to an internet service provider. Client computingdevice 130 may be a smart phone, personal computer, tablet computingdevice, PDA, laptop, set-top boxes, smart televisions, or any othercomputing device capable of transmitting and receiving information andperforming the functions described herein.

In an embodiment, a media player application 122 is stored on clientcomputing device. The media player application 122 may be programmed orconfigured to play digital media files, store portions of digital mediafiles in a buffer, request additional segments of digital media files,and identify a playback timestamp.

In FIG. 1, media player application 122 is depicted as currently playingparticular media file 124. The playback timestamp refers to a currentlocation in the playback of the particular media file. The playedportion of the particular media file 124 refers to a portion of the filethat has already been played through the media player application. Thebuffered portion of the particular media file 124 refers to a portion ofthe particular media file 124 that has been received by media playerapplication but has not been played yet. Finally, the unreceived portionof the particular media file corresponds to one or more remainingsegments of the particular media file 124 that is stored in media filerepository 140 but has not been received by media application 122.

Transcoding server computer 130 may be implemented using a server-classcomputer or other computer having one or more processor cores,co-processors, or other computers. In some embodiments, transcodingserver computer 130 may also include a client computing device, such asa smart phone and/or laptop computer.

FIG. 1 depicts client computing device 120, transcoding server computer130, and media file repository 140 as distinct elements for the purposeof illustrating a clear example. However, in other embodiments more orfewer server computers may accomplish the functions described herein.For example, transcoding server computer 130 may store media filerepository 140 in memory of transcoding server computer 130. As anotherexample, transcoding server computer 130 may interact with a pluralityof client computing devices requesting data from media file repository140. Additionally, media file repository 140 may be any source of adigital media file. For example, the methods described herein may beutilized on a device that streams video as it is being captured.

Each of media transcoding instructions 132, client computing deviceinterface instructions 134, and transcoding quality determinationinstructions 136 comprises a set of one or more pages of main memory,such as RAM, in a server computer into which executable instructionshave been loaded and which, when executed, cause the transcoding servercomputer to perform the functions or operations that are describedherein with reference to those modules. For example, the mediatranscoding instructions 132 may comprise a set of pages in RAM thatcontain instructions which when executed cause performing the mediatranscoding functions that are described herein. The instructions may bein machine executable code in the instruction set of a CPU and may havebeen compiled based upon source code written in JAVA, C, C++,OBJECTIVE-C, or any other human-readable programming language orenvironment, alone or in combination with scripts in JAVASCRIPT, otherscripting languages and other programming source text. The term “pages”is intended to refer broadly to any region within main memory and thespecific terminology used in a system may vary depending on the memoryarchitecture or processor architecture.

In another embodiment, each of media transcoding instructions 132,client computing device interface instructions 134, and transcodingquality determination instructions 136 also may represent one or morefiles or projects of source code that are digitally stored in a massstorage device such as non-volatile RAM or disk storage, in the systemsof FIG. 1 or a separate repository system, which when compiled orinterpreted cause generating executable instructions which when executedcause the computer to perform the functions or operations that aredescribed herein with reference to those modules. In other words, thedrawing figure may represent the manner in which programmers or softwaredevelopers organize and arrange source code for later compilation intoan executable, or interpretation into bytecode or the equivalent, forexecution by the transcoding server computer.

Media transcoding instructions 132 comprise computer readableinstructions in a portion of memory of transcoding server computer 130and which, when executed by one or more processors, cause transcodingserver computer 130 to convert a digital media file from one encoding toanother encoding.

Client computing device interface instructions 134 comprise computerreadable instructions in a portion of memory of transcoding servercomputer 130 and which, when executed by one or more processors, causetranscoding server computer 130 to request data from client computingdevice 120 and send transcoded segments of digital media files to theclient computing device 120.

Transcoding quality determination instructions 136 comprise computerreadable instructions in a portion of memory of transcoding servercomputer 130 and which, when executed by one or more processors, causetranscoding server computer 130 to determine a quality into which totranscode a particular media file based on one or more factors.

Media file repository 140 is a repository of digital media files. Mediafile repository 140 may be stored on a server computer system separatefrom the transcoding server computer 130. The separate server computersystem may be a physical server computer, such a personal server, or avirtual server provisioned in the cloud. The separate server computersystem may communicate with transcoding server computer 130 over network100. Additionally or alternatively, media file repository 140 may bestored in memory of transcoding server computer 130.

Transcoding During File Streaming

In an embodiment, a transcoding server computer adaptively transcodesportions of a digital media file into transcoded media segments ofdifferent qualities. FIG. 2 depicts an example method of adaptivetranscoding of a digital media file.

At step 202, a first portion of a particular media file is received at atranscoding server computer from a media file repository. For example, aclient computing device may request playback of a video file stored onthe transcoding server computer. In response to receiving the requestfrom the client computing device, a transcoding application may requesta first portion of a media file from a media file repository stored onthe transcoding server computer. Additionally or alternatively, thetranscoding server computer may request the first portion of the mediafile from a media file repository stored on a separate server computer.

The first portion of the particular media file may refer to a particularsegment of a plurality of sequential segments of the particular mediafile. For example, a digital movie may be broken up into a plurality often second long segments. The transcoding server computer may requestsegments of the digital media file sequentially, such that a requestedsegment immediately follows a previously requested segment. Thetranscoding server computer may ensure that the received portions of themedia file may conform to one or more media streaming protocols beforesending them to the client computing device. For example, thetranscoding server computer may alter received portions of the mediafile in order to conform to the HTTP Live Streaming (HLS) protocoldefined by Apple Inc. of Cupertino, Calif.

The first portion of the particular media file may refer to any segmentof the plurality of sequential segments. Thus, the first portion of theparticular media file may not be the beginning portion of the mediafile. In some embodiments, the beginning portion of the media file ispre-transcoded and the methods described herein are utilized foron-the-fly transcoding of additional segments of the media file.

At step 204, the first portion of the particular media file istranscoded into a first transcoded media segment of a first quality. Forexample, the transcoding server computer may execute transcodingsoftware, such as a standard H.264 video decoder and encoder, totranscode the first portion of the particular media file into atranscoded media segment of the first quality. The transcoded mediasegment may be a file of a different format, bitrate, resolution, or anycombination thereof. Code for implementing H.264 transcoders as well asother transcoders is available on GitHub.

The first quality may refer to a video bitrate, video resolution, audiobitrate, audio sampling rate, and/or audio channel count. In anembodiment, different transcoders are stored on the transcoding servercomputer, each of which configured to transcode digital media files todifferent bitrates. For example, a first transcoder may be configured totranscode a digital media file to 2 Mbit/s while a second transcoder isconfigured to transcode a digital media file to 4 Mbit/s. Additionallyor alternatively, one or more transcoders may be configured to transcodedigital media files to a plurality of different bitrates. For example, asingle transcoder may be configured to select a bitrate from a pluralityof bitrates for transcoding a file. As another example, a plurality oftranscoders may each be configured to transcode received files to any ofa plurality of bitrates.

At step 206, the first transcoded media segment is transmitted to aclient computing device. For example, the transcoding server computermay transmit the first transcoded media segment over the network to theclient computing device using one or more streaming protocols, such asthe HLS protocols and/or other Dash protocols.

At step 208, a second portion of the particular media file is receivedat the transcoding server computer from the media file repository. Thesecond portion of the particular media file may be a segment of themedia file that is subsequent to the first portion of the particularmedia file. For example, the first portion of the particular media filemay be a ten second segment of the particular media file. The secondportion of the particular media file may be a ten second segment of theparticular media file that plays after the first portion of theparticular media file.

At step 210, the second portion of the particular media file istranscoded into a second transcoded media segment of a second qualitythat is different than the first quality. For example, the transcodingserver computer may use a first transcoder to transcode the firstportion of the media file into a first bitrate and a second transcoderto transcode the second portion of the media file into a second bitratethat is either higher or lower than the first bitrate. As anotherexample, a single transcoder may be configured to transcode the firstportion of the media file into the first bitrate and to transcode thesecond portion of the media file into a second bitrate that is eitherhigher or lower than the first bitrate.

Transcoding the digital media file into different bitrates may compriseexecuting different transcoding algorithms for the digital media files.For example, a first algorithm may transcode an MPEG-2 video file intoan MPEG-4 video file while a second algorithm may transcode the MPEG-2video file into an H.264 video file. As another example, a firstalgorithm may transcode a video file into a first transcoded segmentwith a first resolution while a second algorithm may transcode the videofile into a second transcoded segment with a second resolution.

At step 212, the second transcoded media segment is transmitted to theclient computing device. For example, the transcoding server computermay transmit the second transcoded media segment over the network to theclient computing device using one or more streaming protocols, such asthe HLS protocols and/or other Dash protocols. While the steps ofsending the transcoded segments are listed separately, in an embodimentmultiple transcoded segments are transmitted as a single file. Forexample, the client computing device may join a plurality of segmentstogether as new transcoded segments are produced prior to sending thesegments to the client computing device. Thus, although the servercomputer requests and transcodes separate segments, the client computingdevice may download a full media file instead of downloading discretesegments of a media file.

In an embodiment, the transcoding server computer deletes transcodedmedia segments after sending them to the client computing device. Bydeleting sent transcoded media segments after they have been sent, thetranscoding server computer is able to minimize the amount of datastored on the transcoding server computer. Additionally oralternatively, the transcoding server computer may store one or more ofthe transcoded media segments to use for subsequent plays of the digitalmedia file. Thus, the transcoding server computer may still perform onthe fly transcoding, but use one or more of the stored transcoded mediasegments when the quality of the stored transcoded media segments matchthe quality that the transcoding server computer is sending to theclient computing device.

In an embodiment, the transcoding server computer transcodes portions ofthe digital media file while the client computing device is playingpreviously transcoded segments of the digital media file. For example,during playback of the first transcoded media segment, the transcodingserver computer may begin transcoding of the second portion of thedigital media file. Additionally, one or more portions of the digitalmedia file may be transcoded in between the first and second portions.For example, a third and fourth portion of the digital media file may betranscoded into transcoded segments of the same quality as the firstportion of the digital media file. While one or more of the transcodedsegments are being played, the transcoding server computer may begintranscoding the second portion of the digital media file into atranscoded segment of a different quality.

FIG. 3 depicts an example system executing the methods described herein.While the example of FIG. 3 depicts media file repository 140 asseparate from transcoding server computer 130, in some embodiments,media file repository 140 is stored on transcoding server computer 130and sends segments of the particular media file to one or moretranscoding applications executing on transcoding server computer 130.

In FIG. 3, media file repository 140 stores a particular media file.While the particular media file is broken up into segments fordescriptive purposes, in embodiments the particular media file is storedas a single file that is broken up when it is sent to transcoding servercomputer 130. The darkened segments of the particular media file referto segments of the particular media file that have been sent totranscoding server computer 130. The white segments of the particularmedia file refer to segments of the particular media file that have yetto be sent to transcoding server computer 130.

In FIG. 3, the first and second portions of the particular media fileare sent to transcoding server computer 130. A first transcodingtranscodes the first portion of the media file into a first transcodedmedia segment which is sent to client computing device 120 to be playedthrough media player application 122. A second transcoding transcodesthe second portion of the media file into a second transcoded mediasegment which is sent to client computing device 120 to be stored in abuffer of media player 122 until media player application 122 is readyto play the second transcoded segment.

In an embodiment, the buffer of the media player application 122 maystore a plurality of transcoded media segments. The transcoded mediasegments may comprise different qualities. For example, a first bufferedsegment may comprise a bitrate of 2 Mbit/s while a second bufferedsegment may comprise a bitrate of 4 Mbit/s.

Adaptive Transcoding

In an embodiment, the transcoding server computer transcodes media fileswhen the media files are being used. For example, a client computingdevice may request to view a particular media file that is stored in themedia file repository. At the time the transcoding server computerreceives the request, the transcoding server computer may not be storingany transcoded versions of the particular media file. A transcodingapplication executing on the transcoding server computer may request andreceive portions of the particular media file, transcode them intotranscoded media segments, and send them to the client computing devicewhen ready. Thus, the transcoding application may transcode a portion ofthe media file while the client computing device is playing an earliertranscoded portion of the media file.

In an embodiment, the transcoding server computer may switch fromtranscoding into segments of a first quality to transcoding intosegments of a second quality while the client computing device isplaying earlier portions of the media file. The transcoding servercomputer may be configured to switch qualities based on performance ofthe client computing device. For example, if the transcoding servercomputer determines that the client computing device is capable ofdownloading files of a higher bitrate, the transcoding server computermay switch to transcoding the file into a higher bitrate. Alternatively,if the transcoding server computer determines that the client computingdevice is having trouble downloading files at a current bitrate, thetranscoding server computer may lower the bitrate for transcoding futureportions of the particular media file.

In an embodiment, the transcoding server computer monitors performanceof the client computing device. For example, the transcoding servercomputer may measure a rate at which the client computing devicedownloads transcoded segments of a particular quality. The transcodingserver computer may average the client computing device download speedover a particular period of time, such as the time it takes to downloadone complete segment. Additionally or alternatively, the transcodingserver computer may monitor download speeds for a plurality of smallbursts of time. For example, the transcoding server computer maydetermine how much of a transcoded media file has been downloaded at thestart of a plurality of two second intervals and at the end of theplurality of two second intervals. Based on the amount of data that hasbeen transferred in the two second intervals, the transcoding servercomputer may compute a plurality of different download rates.

In an embodiment, the client computing device monitors its ownperformance and sends its performance data to the transcoding servercomputer. For example, the client computing device may monitor the rateat which it downloads transcoded segments of the digital media file fromthe transcoding server computer. The client computing device may monitora maximum download rate for a transcoded segment, an average downloadrate for a transcoded segment, and/or one or more download ratesoccurring during particular intervals of time. For example, the clientcomputing device may measure the average download rate for each of aplurality of bursts of time. The client computing device may send thedownload rates for each burst of time, the average download rate for theburst of time, and/or a download rate for a burst of time with thehighest download rate.

The transcoding server computer may be programmed or configured totranscode to different qualities based on the performance of the clientcomputing device. For example, if the client computing device downloadsa ten second long segment of a particular media file at a particularbitrate in five seconds, then the transcoding server computer maydetermine that the client computing device is capable of downloadingtranscoded segments of a higher bitrate without adversely affectingplayback of the video.

In an embodiment, the transcoding server computer is programmed orconfigured to transcode to different qualities based on the performanceof the client computing device during particular bursts of time. Forexample, the transcoding server computer may measure a plurality ofdownload rates during a plurality of intervals of times. The pluralityof intervals of times may be as small as a few milliseconds or as largeas multiple seconds. The transcoding server computer may identify aparticular interval of time as being indicative of an overall capabilityof the client computing device. For example, the transcoding servercomputer may select the highest download speed the client computingdevice attained during the plurality of intervals of time.

The transcoding server computer may compute a value indicative of thepossible quality change based on the performance of the client computingdevice. As an example, the server computer may compute a maximum qualityfor the digital media file such that the digital media file is capableof being downloaded as fast as it is played. The maximum quality may becomputed as a product of the current quality and the rate at which dataof the current quality is downloaded. The transcoding server computermay then select the maximum quality as the second quality fortranscoding the digital media file.

In an embodiment, the transcoding server computer incrementally changesthe quality of the transcoded segments based on determinations that theclient computing device is capable of downloading higher or lowerquality versions of the digital media file without interrupting orpausing a current stream. For example, the transcoding server computermay be programmed or configured to increase the bitrate of thetranscoded segments by 1 Mbit/s in response to determining that theclient computing device is capable of downloading the current segmentfaster than the client computing device is playing the digital mediafile. The transcoding server computer may also be programmed orconfigured to decrease the quality of transcoded segments by 2 Mbit/s inresponse to determining that the client computing device is not capableof downloading the current segment as fast as the client computingdevice is playing the digital media file.

By increasing the quality of the transcoded segments incrementally, thetranscoding server computer minimizes the chance that the quality willbe raised so high that the playback of the digital media file on theclient computing device catches up to the end of the downloaded content,thereby disrupting playback of the digital media file. By decreasing thequality of the transcoded segments incrementally, the transcoded servercomputer minimizes the negative impact of quality reduction on theviewer of the digital media file. Additionally, changing the quality ofthe transcoded segments incrementally ensures that the change in qualityis less noticeable to the viewer of the digital media file.

In an embodiment, the transcoding server computer changes the quality ofthe transcoded segments incrementally, but with larger changes forlarger differences in the capabilities of the client computing deviceand the quality of the last transcoded segment. For example, thetranscoding server computer may be programmed or configured to increasethe quality by 2 Mbit/s if the transcoding server computer determinesthat the client computing device is capable of downloading files ofqualities between 2 Mbit/s and 4 Mbit/s higher than the last transcodedsegment without adversely affecting playback of the file. Thetranscoding server computer may be further programmed or configured toinstead increase the quality by 3 Mbit/s if the transcoding servercomputer determines that the client computing device is capable ofdownloading files of qualities between 4 Mbit/s and 5 Mbit/s higher thanthe last transcoded segment without adversely affecting playback of thefile. The differences in quality change based on ranges of capabilitiesallows the transcoding server computer to be more adaptive to theindividual client computing device while still maintaining the benefitsof incremental changes.

The transcoding server computer may use different metrics fordetermining whether to increase the quality of transcoded segments thanfor determining whether to decrease the quality of transcoded segments.In an embodiment, the transcoding server computer increases the qualityof transcoded segments comparatively slower than the transcoding servercomputer decreases the quality of transcoded segments. As an example,the transcoding server computer may increase the quality of transcodedsegments incrementally by 1 Mbit/s, but decrease the quality oftranscoded segments incrementally by 2 Mbit/s. As another example, thetranscoding server computer may increase the quality only if thedifference in quality between the highest download rate quality of theclient computing device and the last transcoded segment is greater thana first threshold value, such as 2 Mbit/s. In contrast, the transcodingserver computer may decrease the quality only if the difference inquality between the last transcoded segment and the highest downloadrate quality of the client computing device is greater than a secondthreshold value that is lower than the first threshold value, such as 1Mbit/s.

By changing the transcoding quality based on the current bandwidthbetween the transcoding server computer and the client computing device,the transcoding server computer adapts to the capabilities of the clientcomputing device, thereby maximizing the quality of video transcodingreceived by the client computing device while minimizing adverse effectson video playback, such as forcing the client computing device to pausethe video while new data is downloaded. Additionally, the transcodingserver computer is able to adapt to changes in capabilities of theclient computing device over time. Thus, if the connection qualitybetween the client computing device and the transcoding server computerchanges, the transcoding server computer is capable of adjusting thequality of the transcoding in response.

In an embodiment, the transcoding server computer transcodes additionalsegments of the digital media file. For example, some transcodingprograms introduce audio and/or visual errors in the beginning of atranscoded media segment. In order to avoid playing transcoded segmentswith errors, the transcoding server computer may begin transcoding priorto the next segment in the digital media file. For example, thetranscoding server computer may initially transcode a first portion of adigital media file into a first quality. When the transcoding servercomputer changes to a second quality for a subsequent portion of thedigital media file, the transcoding server computer may transcode boththe first portion of the digital media file and the subsequent portionof the digital media file into the second quality. The transcodingserver computer may then send a transcoded segment corresponding to thesubsequent portion of the digital media file to the client computingdevice without sending a transcoded segment corresponding to the firstportion of the digital media file. By including a prior transcodedsegment into a subsequent transcoding of a different quality, thetranscoding server computer avoids displaying any errors that occur atthe start of the transcoding.

Buffer Starvation

Many media playback applications have a limited amount of data that canbe stored in a buffer of the media playback application on the clientcomputing device. The client computing device may reduce the speed atwhich data is downloaded from the transcoding server computer as thebuffer of the media playback application fills, thereby reducing theperceived capabilities of the client computing device from theperspective of the transcoding server computer. Additionally, the clientcomputing device may continually request new segments from thetranscoding server computer. In order to limit proliferation of falseinformation based on a reduced download speed, the transcoding servercomputer may limit the amount of information sent to the clientcomputing device. Thus, the transcoding server computer may wait torespond to the client request for new segments in order to reduce theamount of data stored in the client computing device's buffer. Waitingto respond to the client request may include waiting to transcode and/orsend new segments to the client computing device. Additionally oralternatively, the transcoding server computer may limit the amount ofinformation sent to the client computing device by slowing the transferof data from the server computer to the client computing device.

In an embodiment, data identifying the capacity and/or current storageof the buffer is sent from the client computing device to thetranscoding server computer. For example, the client computing devicemay monitor the buffer of the media playback application to determinehow much space is left in the buffer. The transcoding server computermay periodically request data from the client computing device regardingthe current availability in the buffer. In response to receiving therequest from the transcoding server computer, the client computingdevice may send data to the transcoding server computer identifying howmuch space is left in the buffer.

Additionally or alternatively, the transcoding server computer maymonitor how much data is sent to the client computing device. Thetranscoding server computer may additionally request a playbacktimestamp from the client computing device indicating a currenttimestamp in the playback of the digital media file. Based on the amountof data sent to the client computing device and the playback timestamp,the transcoding server computer may estimate how much data is stored inthe buffer. For example, if the client computing device reports that theplayback timestamp is fifteen seconds into a video and the client hasdownloaded three segments of video, each segment comprising ten secondsof video, the transcoding server computer may estimate that fifteenseconds of video are stored in the buffer of the client computingdevice.

The transcoding server computer may store a buffer threshold value forlimiting data sent to the client computing device. If the amount of datathat the transcoding server computer determines is stored in the bufferof the client computing device exceeds the buffer threshold value, thetranscoding server computer may wait to send a next transcoded segmentto the client computing device. When the transcoding server computerdetermines that the amount of data stored in the buffer no longerexceeds the buffer threshold value, the transcoding server computer maysend the next transcoded segment to the client computing device.

The buffer threshold value may be a general value, a device-specificvalue, and/or an application-specific value. For example, thetranscoding server computer may store a general buffer threshold valueof 20 seconds. If the length of video that the transcoding servercomputer determines is stored in the buffer of a client computing deviceis less than 20 seconds, the transcoding server computer may transcodeand send a next segment to the client computing device. Otherwise, thetranscoding server computer may wait to send a next segment until thelength of video in the buffer is less than the buffer threshold value.

In embodiments where the client computing device sends data to thetranscoding server computer identifying the size of the buffer on theclient computing device, the transcoding server computer may base thebuffer threshold value on the size of the buffer on the client computingdevice. For example, the transcoding server computer may use as a bufferthreshold value a value equal to half of the size of the buffer on theclient computing device. Thus, if the buffer on the client computingdevice can hold sixty seconds of video, the transcoding server computermay set thirty seconds of video as the buffer threshold value.

In some embodiments, the transcoding server computer may store dataidentifying a buffer size for different media playback applications.Thus, the transcoding server computer may select buffer threshold valuesfor each media playback application for which the transcoding servercomputer knows the buffer size. When the transcoding server computerbegins sending transcoded segments to a client computing device, thetranscoding server computer may identify the media playback applicationexecuting on the client computing device. Based on the media playbackapplication, the transcoding server computer may identify a bufferthreshold value. For example, the transcoding server computer may selecta buffer threshold value that is equal to half the buffer size. Thus, ifa particular media playback application has a buffer size of sixtyseconds, the transcoding server computer may identify the bufferthreshold value as thirty seconds for the particular media playbackapplication.

In an embodiment, the transcoding server computer reduces the amount ofdata sent to the client computing device by reducing the amount of datasent to the one or more transcoders of the transcoding server computer.For example, the transcoding server computer may use the bufferthreshold value to determine when to request a new segment of thedigital media file be sent to the transcoder from the digital mediarepository. In embodiments where the media file repository is stored onthe transcoding server computer, the transcoding application on thetranscoding server computer may wait to request data from the media filerepository until the amount of data stored in the buffer is below thebuffer threshold value. In embodiments where the media file repositoryis stored on a separate server computer, the transcoding server computermay wait to request a new segment from the separate server computeruntil the amount of data stored in the buffer is below the bufferthreshold value.

While the buffer threshold value is generally described as a singularvalue above which the transcoding server computer does not send newsegments, the buffer threshold value may also be dependent on the sizeof the segment being sent. For example, the transcoding server computermay be programmed or configured to determine how much data will bestored in the buffer after a next segment has been sent and determinewhether that value is above or below a particular value. Thus, thebuffer threshold value may be based, at least in part, on the size ofthe segment being sent and an estimated time it will take the clientcomputing device to download the segment.

By reducing the amount of data stored in the buffer of the clientcomputing device, the transcoding server computer ensures that theclient computing device is attempting to download the digital media fileat the fastest possible rate. Thus, the client computing device will besending more accurate data on the capabilities of the client computingdevice instead of slowing its own download rate in order to ensure thatits buffer does not become overfilled.

In an embodiment, the server computer adjusts the buffer threshold valueto generate bursts of high speed downloads by the client computingdevice. For example, the transcoding server computer may initially set abuffer threshold value of twenty seconds. The transcoding servercomputer may increase the buffer threshold value to thirty seconds andmeasure how long it takes to download the next ten seconds of video. Thetranscoding server computer may reduce the buffer threshold back totwenty seconds afterwards so another burst can be measured at a latertime. By generating the bursts of high speed downloading, the servercomputer is able to measure how long it takes the client computingdevice to download larger sections of video of a particular qualityprior to determining whether to increase or decrease the quality ofvideo sent to the client computing device.

Transcoding Default Values

The transcoding server computer may store a general default transcodingvalue for transcoding digital media files. For example, a defaulttranscoding value of 2 Mbit/s may be set for each client computingdevice. Thus, when a client computing device requests a transcodeddigital media file, the transcoding server computer may begintranscoding the digital media file to a quality of 2 Mbit/s. Thetranscoding server computer may then raise the quality of thetranscoding based on the capabilities of the server computer. Thus, if aclient computing device with a fast internet connection beginsdownloading a digital media file at five times the speed of playback,the transcoding server computer may greatly increase the quality of thetranscoding for the client computing device.

In an embodiment, the transcoding server computer stores defaulttranscoding values for individual client computing devices that overridethe general default transcoding value. For example, a client computingdevice may initially request a default transcoding quality value of 5Mbit/s for the client computing device. When the transcoding servercomputer begins transcoding for the client computing device, thetranscoding server computer may begin transcoding at 5 Mbit/s. If theclient computing device downloads the first one or more transcodedsegments too slowly, the transcoding server computer may reduce thetranscoding quality. If the client computing device downloads the firstone or more transcoded segments too quickly, the transcoding servercomputer may raise the transcoding quality.

In an embodiment, default transcoding values for individual clientcomputing devices may be based on the performance of the clientcomputing device in prior situations. For example, during the firstplayback of a digital media file, the transcoding server computer mayadjust the transcoding quality to match the capabilities of the clientcomputing device. Thus, by the end of the first playback, thetranscoding quality may be reflective of the client computing device'sability to download transcoded digital media files. Thus, when theclient computing device requests a digital media file, the transcodingserver computer may begin transcoding the digital media file into atranscoded segment of a quality at or near the quality of the lasttranscoded segment at the end of the first playback.

The transcoding server computer may also store default transcodingvalues based on the type of connection. For example, a first defaulttranscoding value may be set for Local Area Networks (LAN); a seconddefault transcoding value may be set for Wide Area Networks (WAN), and athird default transcoding value may be set for certain types of internetnetworks. Thus, based on the type of network, the transcoding servercomputer may begin transcoding the digital media file at differentqualities.

In an embodiment, the transcoding server computer uses any combinationof the above described factors to set default transcoding values. Forexample, a default transcoding value may be based on the clientcomputing device and the network type. Thus, a particular clientcomputing device may be associated with a plurality of defaulttranscoding values based on the type of network connection.

The transcoding server computer may also store minimum transcodingvalues indicating a minimum quality for transcoding digital media files.Minimum transcoding values may be set to ensure a minimum level ofquality regardless of the abilities of the client computing device,thereby ensuring that the quality of a transcoded video does not fall sofar as to be unwatchable due to a poor connection of the clientcomputing device. Additionally, the client computing device may set aminimum transcoding value in order to prioritize quality of the videoover immediate accessibility.

Additionally, the transcoding server computer may store maximumtranscoding values indicating a maximum quality for transcoding digitalmedia files. For instance, a client computing device, such as asmartphone, may download files subject to particular data limits. Inorder to ensure that the client computing device does not download toolarge of a file, thereby using a large percentage of allotted data, theclient computing device may set a maximum transcoding value. The maximumtranscoding value may also be dependent on a type of connection. Forexample, a smart phone may set a maximum transcoding value for when thesmart phone is downloading a file over a mobile data connection, but nomaximum transcoding value for when the smart phone is downloading thefile over a Wi-Fi connection.

Maximum transcoding values may also be based on the capabilities of thetranscoding server computer. For example, the transcoding servercomputer may only have bandwidth to upload files of a particular qualityto other devices. Thus, the transcoding server computer may set themaximum transcoding value to the particular quality, thereby ensuringthat the transcoding server computer is capable of uploading thetranscoded files to the client computing device. As the availablebandwidth for the transcoding server computer changes, such as due toconnection problems, the transcoding server computer may change themaximum transcoding value to compensate.

Transcoding Load Balancing

In an embodiment, the transcoding server computer changes transcodingqualities in order to balance a load on the transcoding server computer.The load may refer to a network load and/or use of the resources of thetranscoding server computer. Thus, the transcoding server computer maybase a change in quality on the capabilities of the transcoding servercomputer through either a network load and/or output load, the currentquality of a particular transcoded segment, and a starting transcodingquality for transcoding a second digital media file for a differentclient computing device.

As an example, a transcoding server computer has available bandwidth toupload digital media files with an aggregate quality of 10 Mbit/s at agiven time. A first client computing device begins downloading a digitalmedia file from the transcoding server computer. Overtime, the qualityof the transcoded segments sent to the client computing device increasesto 10 Mbit/s. If a second client computing device requests a digitalmedia file from the transcoding server computer, the transcoding servercomputer may adjust the transcoding quality for the first clientcomputing device in order to free up bandwidth for the second clientcomputing device.

As another example, a server computer may be limited to output based onthe output resolution of a video. For example, the server computer mayhave enough power to output two high definition 1080p video streams. Ifthe transcoding server computer begins performing other tasks and/ortranscoding and sending streams to other devices, the transcoding servercomputer may reduce the quality of the high definition streams based onthe increased load on the server computer's resources.

In an embodiment, the transcoding server computer starts new datastreams at a general minimum transcoding quality and reduces the qualityof a prior transcoded file in order to compensate. For example, in theabove example, the transcoding server computer may store a generaldefault transcoding value of 2 Mbit/s. Thus, the transcoding servercomputer may reduce the quality of the transcoded files sent to thefirst client computing device to 8 Mbit/s, thereby freeing up enoughbandwidth for the transcoding server computer to send files of 2 Mbit/sto the second transcoding server computer.

The transcoding server computer may continue to load balance byincreasing the quality of the transcoded segments sent to the secondclient computing device while reducing the quality of the transcodedsegments sent to the first client computing device. For example, if thetranscoding server computer determines that the second client computingdevice is capable of downloading a digital media file at a qualityhigher than 2 Mbit/s, the transcoding server computer may raise thequality of the transcoded segments for the second client computingdevice while lowering the quality of the transcoded segment for thefirst client computing device.

In an embodiment, the transcoding server computer increases the qualityof transcoded segments for subsequent digital media files up to a limitbased on the quality of a current transcoding of a digital media file.For example, in the above example, the transcoding server computer mayset a limit for increasing the quality of the second digital media fileto 5 Mbit/s, thereby ensuring that the quality of the transcoding of thefirst media file never drops below the quality of the second digitalmedia file.

Additionally or alternatively, the transcoding server computer mayensure that a quality of the transcoding for the first media file doesnot drop below a specified minimum quality for the first digital mediafile. Thus, if a general minimum quality is set at 2 Mbit/s, thetranscoding server computer may raise the quality of the second digitalmedia file to a maximum of 8 Mbit/s, thereby ensuring that the qualityof the first digital media file does not drop below 2 Mbit/s.

In an embodiment, a client computing device may specify one or moredevices and/or streams to be given priority over other devices and/orstreams in terms of quality. In the above example, if the first clientcomputing device sends data to the transcoding server computerrequesting that the first client computing device be prioritized overthe second client computing device, then the transcoding server computermay begin transcoding the second digital media file to a quality of 2Mbit/s without raising the quality based on the capabilities of thesecond client computing device. If the transcoding server computerlowers the quality of the transcoding of the first digital media filedue to the capabilities of the first client computing device changing,then the transcoding server computer may begin to raise the quality ofthe transcoding of the second digital media file. If the transcodingserver computer determines that the first client computing device canhandle a file of a higher quality again, then the transcoding servercomputer may increase the quality of the first digital media file to amaximum quality of 8 Mbit/s and lower the quality of the second digitalmedia file to a minimum of 2 Mbit/s.

The load balancing techniques described herein allow the transcodingserver computer to balance quality of transcoded digital media fileswith capabilities of the transcoding server computer. Thus, as thetranscoding server computer's ability to upload digital media filesincreases, the transcoding server computer may gradually increase thequality of transcoded digital media files. While the above examplesdescribe balancing based on two client computing devices, the loadbalancing techniques described herein may be used with any number ofclient computing devices as long as the transcoding server computer iscapable of sending minimum quality transcoded files to each clientcomputing device. If the transcoding server computer is unable to sendminimum quality transcoded files to each client computing device, thetranscoding server computer may lower the quality of some files belowthe minimum quality, stagger the sending of transcoded segments, and/orselect one or more client computing devices to not receive a transcodeddigital media file.

Hardware Overview

According to one embodiment, the techniques described herein areimplemented by one or more special-purpose computing devices. Thespecial-purpose computing devices may be hard-wired to perform thetechniques, or may include digital electronic devices such as one ormore application-specific integrated circuits (ASICs) or fieldprogrammable gate arrays (FPGAs) that are persistently programmed toperform the techniques, or may include one or more general purposehardware processors programmed to perform the techniques pursuant toprogram instructions in firmware, memory, other storage, or acombination. Such special-purpose computing devices may also combinecustom hard-wired logic, ASICs, or FPGAs with custom programming toaccomplish the techniques. The special-purpose computing devices may bedesktop computer systems, portable computer systems, handheld devices,networking devices or any other device that incorporates hard-wiredand/or program logic to implement the techniques.

For example, FIG. 4 is a block diagram that illustrates a computersystem 400 upon which an embodiment may be implemented. Computer system400 includes a bus 402 or other communication mechanism forcommunicating information, and a hardware processor 404 coupled with bus402 for processing information. Hardware processor 404 may be, forexample, a general purpose microprocessor.

Computer system 400 also includes a main memory 406, such as a randomaccess memory (RAM) or other dynamic storage device, coupled to bus 402for storing information and instructions to be executed by processor404. Main memory 406 also may be used for storing temporary variables orother intermediate information during execution of instructions to beexecuted by processor 404. Such instructions, when stored innon-transitory storage media accessible to processor 404, rendercomputer system 400 into a special-purpose machine that is customized toperform the operations specified in the instructions.

Computer system 400 further includes a read only memory (ROM) 408 orother static storage device coupled to bus 402 for storing staticinformation and instructions for processor 404. A storage device 410,such as a magnetic disk, optical disk, or solid-state drive is providedand coupled to bus 402 for storing information and instructions.

Computer system 400 may be coupled via bus 402 to a display 412, such asa cathode ray tube (CRT), for displaying information to a computer user.An input device 414, including alphanumeric and other keys, is coupledto bus 402 for communicating information and command selections toprocessor 404. Another type of user input device is cursor control 416,such as a mouse, a trackball, or cursor direction keys for communicatingdirection information and command selections to processor 404 and forcontrolling cursor movement on display 412. This input device typicallyhas two degrees of freedom in two axes, a first axis (e.g., x) and asecond axis (e.g., y), that allows the device to specify positions in aplane.

Computer system 400 may implement the techniques described herein usingcustomized hard-wired logic, one or more ASICs or FPGAs, firmware and/orprogram logic which in combination with the computer system causes orprograms computer system 400 to be a special-purpose machine. Accordingto one embodiment, the techniques herein are performed by computersystem 400 in response to processor 404 executing one or more sequencesof one or more instructions contained in main memory 406. Suchinstructions may be read into main memory 406 from another storagemedium, such as storage device 410. Execution of the sequences ofinstructions contained in main memory 406 causes processor 404 toperform the process steps described herein. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions.

The term “storage media” as used herein refers to any non-transitorymedia that store data and/or instructions that cause a machine tooperate in a specific fashion. Such storage media may comprisenon-volatile media and/or volatile media. Non-volatile media includes,for example, optical disks, magnetic disks, or solid-state drives, suchas storage device 410. Volatile media includes dynamic memory, such asmain memory 406. Common forms of storage media include, for example, afloppy disk, a flexible disk, hard disk, solid-state drive, magnetictape, or any other magnetic data storage medium, a CD-ROM, any otheroptical data storage medium, any physical medium with patterns of holes,a RAM, a PROM, and EPROM, a FLASH-EPROM, NVRAM, any other memory chip orcartridge.

Storage media is distinct from but may be used in conjunction withtransmission media. Transmission media participates in transferringinformation between storage media. For example, transmission mediaincludes coaxial cables, copper wire and fiber optics, including thewires that comprise bus 402. Transmission media can also take the formof acoustic or light waves, such as those generated during radio-waveand infra-red data communications.

Various forms of media may be involved in carrying one or more sequencesof one or more instructions to processor 404 for execution. For example,the instructions may initially be carried on a magnetic disk orsolid-state drive of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 400 canreceive the data on the telephone line and use an infra-red transmitterto convert the data to an infra-red signal. An infra-red detector canreceive the data carried in the infra-red signal and appropriatecircuitry can place the data on bus 402. Bus 402 carries the data tomain memory 406, from which processor 404 retrieves and executes theinstructions. The instructions received by main memory 406 mayoptionally be stored on storage device 410 either before or afterexecution by processor 404.

Computer system 400 also includes a communication interface 418 coupledto bus 402. Communication interface 418 provides a two-way datacommunication coupling to a network link 420 that is connected to alocal network 422. For example, communication interface 418 may be anintegrated services digital network (ISDN) card, cable modem, satellitemodem, or a modem to provide a data communication connection to acorresponding type of telephone line. As another example, communicationinterface 418 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN. Wireless links may also beimplemented. In any such implementation, communication interface 418sends and receives electrical, electromagnetic or optical signals thatcarry digital data streams representing various types of information.

Network link 420 typically provides data communication through one ormore networks to other data devices. For example, network link 420 mayprovide a connection through local network 422 to a host computer 424 orto data equipment operated by an Internet Service Provider (ISP) 426.ISP 426 in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the“Internet” 428. Local network 422 and Internet 428 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link 420and through communication interface 418, which carry the digital data toand from computer system 400, are example forms of transmission media.

Computer system 400 can send messages and receive data, includingprogram code, through the network(s), network link 420 and communicationinterface 418. In the Internet example, a server 430 might transmit arequested code for an application program through Internet 428, ISP 426,local network 422 and communication interface 418.

The received code may be executed by processor 404 as it is received,and/or stored in storage device 410, or other non-volatile storage forlater execution.

In the foregoing specification, embodiments have been described withreference to numerous specific details that may vary from implementationto implementation. The specification and drawings are, accordingly, tobe regarded in an illustrative rather than a restrictive sense. The soleand exclusive indicator of the scope of the disclosure, and what isintended by the applicants to be the scope of the disclosure, is theliteral and equivalent scope of the set of claims that issue from thisapplication, in the specific form in which such claims issue, includingany subsequent correction.

1. A method comprising: receiving, at a transcoding server computer, afirst portion of a particular media file from a media file repository;transcoding the first portion of the particular media file into a firsttranscoded media segment of a first quality; transmitting the firsttranscoded media segment to a client computing device; aftertransmitting the first transcoded media segment to the client computingdevice: receiving, at the transcoding server computer, a second portionof the particular media file from the media file repository; determiningthat the second portion of the particular media file is to be transcodedto a media segment of a second quality instead of a media segment of thefirst quality and, in response, transcoding the second portion of theparticular media file to a second transcoded media segment of the secondquality that is different than the first quality instead of transcodingthe second portion of the particular media file to a second transcodedmedia segment of the first quality; sending the second transcoded mediasegment to the client computing device.
 2. The method of claim 1,further comprising: identifying, at the transcoding server computer, aparticular download speed for the client computing device; based on theparticular download speed, selecting the second quality; performing thetranscoding of the second portion of the particular media file inresponse to selecting the second quality.
 3. The method of claim 2,further comprising: monitoring a rate at which the client computingdevice downloads the first transcoded media segment; wherein theparticular download speed is based, at least in part, on the monitoredrate.
 4. The method of claim 2, further comprising: receiving, from theclient computing device, data identifying a maximum download speed forthe first transcoded media segment; wherein the particular downloadspeed is based, at least in part, on the received data.
 5. The method ofclaim 2, further comprising determining that the particular downloadspeed is higher than a particular value and, in response, identifyingthe second quality as a higher quality than the first quality.
 6. Themethod of claim 2, further comprising determining that the particulardownload speed is lower than a particular value and, in response,identifying the second quality as a lower quality than the firstquality.
 7. The method of claim 1, further comprising: storing, at thetranscoding server computer, a buffer threshold value; receiving, fromthe client computing device, first playback data identifying a firstplayback timestamp; determining that a first difference between atranscoded amount of the particular media file sent to the clientcomputing device and the first playback timestamp exceeds the bufferthreshold value and, in response, waiting to request a third portion ofthe particular media file; receiving, from the client computing device,second playback data identifying a second playback timestamp;determining that a second difference between the transcoded amount ofthe particular media file sent to the client computing device and thesecond playback timestamp does not exceed the buffer threshold valueand, in response, requesting the third portion of the particular mediafile from the media file repository.
 8. The method of claim 1, whereinthe media file repository is stored on a particular computing deviceseparate from the transcoding server computer.
 9. The method of claim 1,further comprising: determining one or more initial capabilities of thetranscoding server computer prior to transcoding the first portion ofthe particular media file; determining one or more altered capabilitiesof the transcoding server computer prior to transcoding the secondportion of the particular media file; selecting the second qualitybased, at least in part, on the one or more altered capabilities of thetranscoding server computer.
 10. The method of claim 1, furthercomprising: receiving a request from a second client computing device toaccess a second media file from the media file repository; determining athird quality for transcoding the second media file; determining thesecond quality based, at least in part, on the third quality and one ormore capabilities of the transcoding server computer.
 11. The method ofclaim 10, further comprising: receiving, at the transcoding servercomputer, a first portion of the second media file; transcoding thefirst portion of the second media file into a third transcoded mediasegment of the third quality; transmitting the third transcoded mediasegment to the second client computing device; determining a fourthquality for transcoding the second media file; determining a fifthquality for transcoding the particular media file based, at least inpart, on the fourth quality and the one or more capabilities of thetranscoding server computer; receiving a third portion of the particularmedia file; transcoding the third portion of the particular media fileinto a fourth transcoded media segment of the fifth quality;transmitting the fourth transcoded media segment to the client computingdevice.
 12. The method of claim 1, wherein transcoding the secondportion of the particular media file into the second transcoded mediasegment comprises: transcoding the first portion of the particular mediafile with the second portion of the particular media file into acombined transcoded media segment; separating the second transcodedmedia segment from the combined transcoded media segment.
 13. Acomputing system comprising: one or more processors a memory, coupled tothe one or more processors, storing instructions which, when executed bythe one or more processors, cause performance of: receiving a firstportion of a particular media file from a media file repository;transcoding the first portion of the particular media file into a firsttranscoded media segment of a first quality; transmitting the firsttranscoded media segment to a client computing device; aftertransmitting the first transcoded media segment to the client computingdevice: receiving a second portion of the particular media file from themedia file repository; determining that the second portion of theparticular media file is to be transcoded to a media segment of a secondquality instead of a media segment of the first quality and, inresponse, transcoding the second portion of the particular media file toa second transcoded media segment of [[a]]the second quality that isdifferent than the first quality instead of transcoding the secondportion of the particular media file to a second transcoded mediasegment of the first quality; sending the second transcoded mediasegment to the client computing device.
 14. The computing system ofclaim 13, wherein the instructions, when executed by the one or moreprocessors, further cause performance of: identifying, at thetranscoding server computer, a particular download speed for the clientcomputing device; based on the particular download speed, selecting thesecond quality; performing the transcoding of the second portion of theparticular media file in response to selecting the second quality. 15.The computing system of claim 14, wherein the instructions, whenexecuted by the one or more processors, further cause performance of:monitoring a rate at which the client computing device downloads thefirst transcoded media segment; wherein the particular download speed isbased, at least in part, on the monitored rate.
 16. The computing systemof claim 14, wherein the instructions, when executed by the one or moreprocessors, further cause performance of: receiving, from the clientcomputing device, data identifying a maximum download speed for thefirst transcoded media segment; wherein the particular download speed isbased, at least in part, on the received data.
 17. The computing systemof claim 14, wherein the instructions, when executed by the one or moreprocessors, further cause performance of determining that the particulardownload speed is higher than a particular value and, in response,identifying the second quality as a higher quality than the firstquality.
 18. The computing system of claim 14, wherein the instructions,when executed by the one or more processors, further cause performanceof determining that the particular download speed is lower than aparticular value and, in response, identifying the second quality as alower quality than the first quality.
 19. The computing system of claim13, wherein the instructions, when executed by the one or moreprocessors, further cause performance of: storing a buffer thresholdvalue; receiving, from the client computing device, first playback dataidentifying a first playback timestamp; determining that a firstdifference between a transcoded amount of the particular media file sentto the client computing device and the first playback timestamp exceedsthe buffer threshold value and, in response, waiting to request a thirdportion of the particular media file; receiving, from the clientcomputing device, second playback data identifying a second playbacktimestamp; determining that a second difference between the transcodedamount of the particular media file sent to the client computing deviceand the second playback timestamps does not exceed the buffer thresholdvalue and, in response, requesting the third portion of the particularmedia file from the media file repository.
 20. The computing system ofclaim 13, wherein the media file repository is stored on a particularcomputing device separate from the computing system.
 21. The computingsystem of claim 13, wherein the instructions, when executed by the oneor more processors, further cause performance of: determining one ormore initial capabilities of the computing system prior to transcodingthe first portion of the particular media file; determining one or morealtered capabilities of the computing system prior to transcoding thesecond portion of the particular media file; selecting the secondquality based, at least in part, on the one or more altered capabilitiesof the computing system.
 22. The computing system of claim 13, whereinthe instructions, when executed by the one or more processors, furthercause performance of: receiving a request from a second client computingdevice to access a second media file from the media file repository;determining a third quality for transcoding the second media file;determining the second quality based, at least in part, on the thirdquality and one or more capabilities of the computing system.
 23. Thecomputing system of claim 22, wherein the instructions, when executed bythe one or more processors, further cause performance of: receiving afirst portion of the second media file; transcoding the first portion ofthe second media file into a third transcoded media segment of the thirdquality; transmitting the third transcoded media segment to the secondclient computing device; determining a fourth quality for transcodingthe second media file; determining a fifth quality for transcoding theparticular media file based, at least in part, on the fourth quality andthe one or more capabilities of the computing system; receiving a thirdportion of the particular media file; transcoding the third portion ofthe particular media file into a fourth transcoded media segment of thefifth quality; transmitting the fourth transcoded media segment to theclient computing device.
 24. The computing system of claim 13, whereintranscoding the second portion of the particular media file into thesecond transcoded media segment comprises: transcoding the first portionof the particular media file with the second portion of the particularmedia file into a combined transcoded media segment; separating thesecond transcoded media segment from the combined transcoded mediasegment.